Treatment of tailings streams

ABSTRACT

A process for the treating a mature fine tailings stream is provided. Treatment comprises contacting an alkali metal silicate or polysilicate microgel and an activator with mature fine tailings, entrapping the sand and clay fines within a polysilicate microgel, spreading the silica microgel over a surface, and allowing the silica microgel to dry, and producing a trafficable surface.

FIELD OF THE INVENTION

The present invention relates to a process for extraction of bitumenfrom oil sands, flocculation/dewatering of tailings after extraction,and treatment of tailings streams.

BACKGROUND OF THE INVENTION

Oil sands have become an attractive source of oil recovery to supportglobal demand for oil. Oil sands are large deposits of naturallyoccurring mixtures of bitumen, water, sand, clays, and other inorganicmaterials found on the earth's surface. Bitumen is a highly viscous formof crude oil. The largest oil sands deposits are found in Canada andVenezuela. In particular, the Athabasca oil sands deposit is equivalentto 1.6 to 2.7 trillion barrels of oil, and is located in the Canadianprovinces of Alberta and Saskatchewan. About 10% of the Athabasca oilsands deposit can be mined. Once the oil sands are mined, it isprocessed by extracting the bitumen.

The bitumen must be extracted and separated from the water, sand andfine clays of the oil sands. Today, the oil sands are mined, crushed,then mixed with hot water, and optionally chemicals, to facilitateextracting the bitumen from the sand and clay fines. The extractedbitumen is separated from the sands and fine clays and is then refined.The remaining sand, clays and water, commonly referred to as “tailings”,are further processed to dewater the sand and clays. The sand and clayare typically disposed, e.g., in a tailings pond and settle to becomemature fine tailings. Mature fine tailings are a stable slurrycomprising fine clays and sands, silt, water, and bitumen. Mature finetailings have no strength, no vegetative potential and may be toxic toanimal life, so must be confined and prevented from contaminating watersupplies. The recovered water from the dewatering step may be re-used inthe extraction process. Faster recovery of the water reduces heat energyrequirements when this water is recycled for use in the extractionprocess.

The recovered bitumen from this process is in the form of a froth. Thefroth comprises a concentrated bitumen (typically 50% or greater),water, fine clays and sands. The froth is treated in a froth treatmentunit, which may use steam (to de-aerate the froth) and a naphthenic orparaffinic solvent to recover a bitumen with greater than 95% purity. Abyproduct of the froth treatment process is a froth treatment tailings.The froth treatment tailings comprise water, residual solvent, and finesolids that are primarily smaller than 44 micrometres in size. The frothtreatment tailings are typically disposed of in a tailings pond. Frothtreatment tailings contribute to mature fine tailings formation.

Tipman et al., in U.S. Pat. No. 5,876,592, disclose recovery of bitumenfrom oil sands in a process comprising adding aqueous caustic to an oilsands slurry, to create an emulsion. The emulsion is allowed to separateinto 3 layers, with a top layer of a first froth comprising bitumen,bottom layer, referred to as tailings, comprising water, sand and clayfines that settled, and a middle layer, referred to as middlings,comprising residual bitumen, suspended clay fines and water. Themiddlings are further processed to recover additional bitumen in thesame manner as the oil sands slurry, producing a second froth. Thesecond froth may be combined with the first froth to recover bitumen bydilution with a solvent and removal of sand and clay fines.

Yuan, et al., Canadian Metallurgical Quarterly, 2007, vol. 46, no. 3 pp.265-272, disclose using a multiple-step process, in a particularsequence, for removing sands and fine clays from tailings. The firststep is referred to as flocculation-coagulation-flocculation (FCF), inwhich a flocculant is added. This allows for the flocculation of largerparticles leaving fines in solution. In the second step, a coagulant isadded. The coagulant destabilizes the fines causing small flocs to form.In the third step, a small amount of flocculant is added to combine thelarger flocs from the first step with the smaller flocs in the secondstep, resulting in even larger flocs and an increase of settling rates,allowing for faster dewatering.

Acidified silicate has been used to enhance bitumen extraction byMasliyah, Ind. Eng. Chem. Res., 2005, vol. 44, pp. 4753-4761. Byacidifying the silicates, divalent metal ions can be sequesteredallowing for improved bitumen liberation while maintaining consistentpH. There is a similar disadvantage with this process as found in WO2005/028592, that is, solids are dispersed.

Li, Energy & Fuels, 2005, vol. 19, pp. 936-943 disclose the effect of ahydrolyzed polyacrylamide (HPAM) on bitumen extraction and tailingstreatment of oil sands ores. Careful control of HPAM dosage is necessaryto achieve efficiency in both bitumen extraction and in flocculation ofsolid fines.

Chaiko et al., in U.S. Pat. No. 6,153,103, disclose a method to separateand recover ultra fine particles and soluble salts from a dilute processstreams using sodium silicates and organic gelling agents throughsyneresis process. This method is used for dilute solutions and forsolids to silicate ratios of 0.4:1 or less.

Separation of bitumen from sand and clay fines, as well as dewatering ofthe sand and clay fines for disposal, are especially difficult forso-called “poor quality ores.” Generally, a poor quality ore, inreference to an oil sands ore is an oil sands ore that contains a largeamount of fines that hinder, not only extraction of bitumen, but alsothe dewatering process of sand and clay fines. Poor quality ores aredifficult to extract bitumen from at acceptable yields usingconventional methods. In addition, more bitumen is retained in thetailings streams from extraction of poor quality ores, which is sent tothe tailings pond as a yield loss.

Poor quality ores reduce yield by as much as 35 to 50% and are avoidedwhen possible. Alternatively, poor quality ores are blended in limitedquantities with good quality ores so they can be processed moreeffectively. With demand for oil increasing every year, there is a needto mine these poor quality ores and to produce high yield of bitumen.The tailings should be essentially free of bitumen and separated fromwater, so the water can be re-used and the solids can be returned to theenvironment free of bitumen, within environmental limits.

There is a desire to have lower extraction temperatures (for example,less than about 50° C.) to save heat energy. For example, when anadjacent upgrading facility to treat the extracted bitumen is notavailable, there is added cost to supply heat energy for the extractionwater.

Mature fine tailings ponds also pose an environmental concern. Oftendisposal of the tailings creates ponds where the clays and fines remainsuspended in water and ultimately become mature fines tailings. TheEnergy Resources Conservation Board of Canada has issued Directive 074,which mandates a reduction of fine tailings ponds and the formation oftrafficable deposits for all oil sands operators. Currently, thesemature fine tailings are treating with gypsum/lime and centrifuging.Gypsum/lime treatment is undesirable due to the added calcium ions inand around the tailings pond and the remaining solids are too soft to betrafficable for long periods of time. Centrifuging is undesirable due tothe large capital investment and having to transport the mature finetailings to centrifuge locations.

While there have been many advances in the oil sands extraction andtailings, there remains a need to improve bitumen recovery (yield) fromoil sands, improve de-watering of the tailings (i.e., less water in thetailings) and reduce need to add fresh water bitumen recovery processes.There is also a need to improve bitumen extraction in poor quality ores,and to do so without significant capital equipment, without significantbitumen yield loss. There is also a need to reduce or eliminate maturefine tailings ponds where the remaining solid can be useful. The presentinvention meets these needs.

SUMMARY OF THE INVENTION

The present invention is a process for the extraction/recovery ofbitumen from oil sands and for the treatment of tailings. In oneembodiment of this invention, the process comprises (a) providing anaqueous slurry of an oil sands ore and (b) contacting the slurry with apolysilicate microgel to produce a froth comprising bitumen and atailings stream comprising sand and clay fines. Preferably, the processfurther comprises (c) dewatering the tailings. Bitumen is recovered fromthe froth. Optionally, an anionic polyacrylamide and/or caustic, such assodium hydroxide, sodium silicate, sodium citrate, may be added afterstep (b) and prior to step (c). Alternatively, a polyacrylamide and oneor both of (i) a multivalent metal compound and (ii) a low molecularweight cationic organic polymer may be added after step (b) and beforestep (c). Surprisingly, the process improves recovery of bitumen anddoes not adversely affect flocculation of tailings as compared to use ofsodium silicate instead of polysilicate microgel. The polysilicatemicrogel is carried through to a dewatering step and may enhanceflocculation in said tailings.

In an alternative embodiment of this invention, there is a process fortreating a tailings stream comprising water, sand and clay fines toflocculate the sand and clay fines wherein the process comprises (a)contacting a polysilicate microgel, an anionic polyacrylamide and one orboth of (i) a multivalent metal compound and (ii) a low molecular weightcationic organic polymer with the tailings stream to produce aflocculated solid, and (b) separating the flocculated solid from thestream. Unexpectedly and advantageously, in this second embodiment,flocculation is enhanced compared to use of polyacrylamide alone.

In a third alternative embodiment of this invention, there is a processfor the treating a tailings stream comprising (a) contacting a silicatesource and an activator with said tailings stream, (b) entrapping thefine clay and sand within a silica gel, (c) spreading the silica gelover a surface, and (d) allowing the silica gel to dry, to produce atrafficable surface, wherein the silicate source is an alkali metalsilicate, polysilicate microgel, or combinations thereof and wherein thetailings stream comprises water, fine clays and sands, wherein 20% byvolume to about 100% by volume of the fine clays and sand have aparticle size less than 0.05 mm. Optionally, the tailings stream furthercomprises polysilicate microgels. Optionally the treated tailingsproduced after step (b) can be centrifuged or subjected to other knowndewatering techniques prior to spreading the entrapped fine clays andsand over a surface.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a process flow diagram of a bitumen extraction process andtailings flocculation in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

In a first embodiment of this invention, there is provided a process forthe recovery of bitumen from oil sands which comprises providing anaqueous slurry of an oil sands ore and contacting the slurry with apolysilicate microgel to improve bitumen separation, producing a frothand a tailings. A slurry of an oil sands ore may be produced by miningan oil sands ore, crushing the ore and adding water to produce a slurry.Optionally, an anionic polyacrylamide and/or caustic, such as sodiumhydroxide, sodium silicate and sodium citrate, may be added to thecombination of oil sands ore and microgel. The froth comprises bitumen,clay fines and water. The tailings comprise sand, clay fines, unreactedpolysilicate microgel and water. Preferably the process furthercomprises dewatering the tailings. The polysilicate microgel in thetailings may be carried through with the water to a dewatering step,wherein the microgel may enhance flocculation in the tailings.

In an alternative embodiment, there is provided a process for theflocculation of a tailings stream wherein the tailings stream isproduced from an oil sands ore and comprises water, sand and clay fines.This process comprises contacting the tailings stream with apolysilicate microgel, an anionic polyacrylamide and one or both of amultivalent metal compound and low molecular weight cationic organicpolymer to flocculate the solids.

In a third alternative embodiment of this invention, there is a processfor treating a tailings stream comprising (a) contacting a silicatesource and an activator with said tailings stream, (b) entrapping thefine clay and sand within a silica gel, (c) spreading the silica gelover a surface, and (d) allowing the silica gel to dry to produce atrafficable surface, wherein the silicate source is an alkali metalsilicate, polysilicate microgel, or combinations thereof and wherein thetailings stream comprises water, fine clays and sands, wherein 20% byvolume to about 100% by volume of the fine clays and sand have aparticle size less than 0.05 mm. Optionally, the tailings stream furthercomprises polysilicate microgels. Optionally the treated tailings fromstep (b) can be centrifuged or subjected to other known dewateringtechniques prior to spreading the entrapped fine clays and sand over asurface.

Oil Sands Ore

Oil sands ores are large deposits of naturally occurring mixturescomprising bitumen, sand, clays, and other inorganic materials. Herein,bitumen refers to hydrocarbons and other oils found in oil sands, tarsands, crude oil and other petroleum sources. The oil sands ores used inthis invention are mined materials and typically comprise about 5 to 15wt % bitumen. The oil sands ores further comprise water, sand and clayfines. Generally the oil sands ores comprise about 2 to 5 wt % water.

Inorganic material can be naturally-occurring ores, such as titaniumores and zirconium ores that are present in the oil sands ore.

The process of this invention may be used advantageously to treat poorquality ores. The “poorer” the quality of the oil sands ore, the higherthe level of clay fines. Surprisingly, the process of this invention iseffective at extracting bitumen from poor quality oil sands ores, whileeffectively dewatering the tailings streams.

Poor quality ores are defined herein as an oil sands ore which has oneor more of the following properties: (a) levels of clay fines of greaterthan 15%; (b) montmorillonite clay in an amount greater than 1 wt % ofthe total weight of the oil sands ore, (c) greater than 10 ppm ofcalcium, magnesium; and (d) ores less than 25 meters from the earth'ssurface that have been subject to oxidation.

Polysilicate Microgel

The process of this invention comprises contacting a polysilicatemicrogel with an oil sands ore. Polysilicate microgels are aqueoussolutions which are formed by the partial gelation of an alkali metalsilicate or a polysilicate, such as sodium polysilicate. The microgels,which can be referred to as “active” silica, in contrast to commercialcolloidal silica, comprise solutions of from 1 to 2 nm diameter linkedsilica particles which typically have a surface area of at least about750 m²/g. Polysilicate microgels are commercially available from E. I.du Pont de Nemours and Company, Wilmington, Del.

Polysilicate microgels have SiO₂:Na₂O mole ratios of 4:1 to about 25:1,and are discussed on pages 174-176 and 225-234 of “The Chemistry ofSilica” by Ralph K. Iler, published by John Wiley and Sons, N.Y., 1979.General methods for preparing polysilicate microgels are described inU.S. Pat. No. 4,954,220, the teachings of which are incorporated hereinby reference.

Polysilicate microgels include microgels that have been modified by theincorporation of alumina into their structure. Such alumina-modifiedpolysilicate microgels are referred as polyaluminosilicate microgels andare readily produced by a modification of the basic method forpolysilicate microgels. General methods for preparingpolyaluminosilicate microgels are described in U.S. Pat. No. 4,927,498,the teachings of which are incorporated herein by reference.

Polysilicic acid is a form of a polysilicate microgel and generallyrefers to those silicic acids that have been formed and partiallypolymerized in the pH range 1-4 and comprise silica particles generallysmaller than 4 nm diameter, which thereafter polymerize into chains andthree-dimensional networks. Polysilicic acid can be prepared, forexample, in accordance with the methods disclosed in U.S. Pat. No.5,127,994, incorporated herein by reference.

In addition to the above-described silica microgels, the term“polysilicate microgels” as used herein, includes silica sols having alow S value, such as an S value of less than 50%. “Low S-value silicasols” are described in European patents EP 491879 and EP 502089. EP491879 describes a silica sol having an S value in the range of 8 to 45%wherein the silica particles have a specific surface area of 750 to 1000m²/g, which have been surface modified with 2 to 25% alumina. EP 502089describes a silica sol having a molar ratio of SiO₂ to M₂O, wherein M isan alkali metal ion and/or an ammonium ion of 6:1 to 12:1 and containingsilica particles having a specific surface area of 700 to 1200 m²/g.

Polyacrylamide

Polyacrylamides (PAMs) useful in the present invention include anionic,cationic, non-ionic and amphoteric polyacrylamides. Polyacrylamides arepolymers formed by polymerization of acrylamide, CH₂═CHC(O)NH₂.Polyacrylamides of the present invention typically have a molecularweight greater than one million.

Preferably the PAM is an anionic polyacrylamide (APAM) or cationicpolyacrylamide (CPAM). APAM and CPAM are the generic names for a groupof very high molecular weight macromolecules produced by thefree-radical polymerization of acrylamide and an anionically or acationically charged co-monomer. APAM and CPAM can be prepared bytechniques known to those skilled in the art, including but not limitedto the Mannich reaction. Both the charge density (ionicity) and themolecular weight can be varied in APAM and CPAM. By varying theacrylamide/ionic monomer ratio, a charge density from 0 (nonionic) to100% along the polymer chain can be obtained. The molecular weight isdetermined by the type and concentration of the reaction initiator andthe reaction parameters.

Low Molecular Weight Cationic Organic Polymers

Low molecular weight cationic organic polymers which can be used in thisinvention have a number average molecular weight less than 1,000,000.Preferably, the molecular weight is in the range between about 2,000 toabout 500,000, more preferably between 10,000 and 500,000. The lowmolecular weight polymer is typically selected from the group consistingof polyethylene imine, polyamine, polycyandiamide formaldehyde polymer,diallyl dimethyl ammonium chloride polymer, diallylaminoalkyl(meth)acrylate polymer, dialkylaminoalkyl (meth)acrylamide polymer, acopolymer of acrylamide and diallyl dimethyl ammonium chloride, acopolymer of acrylamide and diallylaminoalkyl (meth)acrylate, acopolymer of acrylamide and dialkyldiaminoalkyl (meth)acrylamide, and acopolymer of dimethylamine and epichlorohydrin. Such polymers aredescribed, for example, in U.S. Pat. Nos. 4,795,531 and 5,126,014. Lowmolecular weight cationic organic polymers are commercially available,for example, from SNF Floerger, Andrézieux, France as FLOQUAT FL 2250and FLOQAUT FL 2449 and from FCT-Water Treatment, Greeley, Colo. asWT-530.

Multivalent Metal Compounds

Multivalent metal compounds useful in the present inventive process arecompounds of metals with more than one valence state. Examples ofmultivalent metals include calcium, magnesium, aluminum, iron, titanium,zirconium and combinations thereof. Preferably, the multivalent metalcompound is soluble in water and is used as an aqueous solution.Examples of suitable multivalent metal compounds include calciumchloride, calcium sulfate, calcium hydroxide, aluminum sulfate,magnesium sulfate, and aluminum chloride, polyaluminum chloride,polyaluminum sulfate, and aluminum chlorohydrate. Preferably themultivalent metal compound is calcium sulfate, aluminum sulfate,polyaluminum sulfate, polyaluminum chloride, aluminum chlorohydrate.Compounds of multivalent metals that are polymerized are especiallyuseful in the present invention.

Activator

Activators in the current invention comprise any compound or mixture ofcompounds that will initiate gelation of the alkali metal silicates.Activators can include acids, alkaline earth metal and aluminum salts,and organic esters, dialdehydes, organic carbonates, organic phosphates,amides, and combinations thereof. Examples of acids useful as activatorsinclude, but not limited to, sulfuric acid, carbon dioxide, phosphoricacid, sodium phosphate, sodium bicarbonate, hydrochloric acid, sodiumhydrogen sulfate, and acetic acid. Examples of alkaline earth metal andaluminum salts include, but not limited to, calcium chloride, calciumoxide, calcium carbonate, calcium sulfate, magnesium sulfate, magnesiumchloride, aluminum sulfate, sodium aluminate. Examples of organicesters, dialdehydes, organic carbonates, organic phosphates, and amidesinclude, but not limited to, acetic esters of glycerol, glyoxal,ethylene carbonate, propylene carbonate, and formamide. Preferably, theactivator is an acid, an alkaline earth metal salt, or combinationsthereof. Preferred acids are sulfuric acid or carbon dioxide. Preferredalkaline earth metal salts are calcium sulfate and calcium chloride. Oneor more activators may be used.

Extraction and Flocculation

Oil sands ores are generally mined from the earth and processed toremove the bitumen, which can then be further treated as a crude oil. Ina first embodiment, an oil sands ore is provided. The oil sands ore ismined from an oil sand deposit and crushed to provide a materialsuitable for extracting bitumen from the ore. Conventional methods canbe used for mining and crushing. The oil sands ore is generallyprocessed as an aqueous slurry. Recycled water from downstreamdewatering step vida infra may be used to prepare the oil sands oreaqueous slurry.

The process of this invention comprises providing an aqueous slurry ofan oil sands ore and contacting the slurry with a polysilicate microgelto extract bitumen from the oil sands ore. Water and optionally air maybe added to the slurry prior to or during this contacting (extraction)step at a temperature in the range of 25 to 90° C. (77 to 194° F.),preferably at a temperature of 35 to 85° C. (95 to 185° F.).Advantageously the contacting step is performed at a temperature of 50°C. or less, for example, 35-50° C. (95-122° F.).

The amounts of the slurry components can vary. An aqueous slurry of anoil sands ore can be prepared by contacting an oil sands ore with waterin an amount of 10% to 500%, based on the mass of the ore, preferably,50% to 200%. The water may be recycled water from the extractionprocess. The amount of water added may be determined by extractionefficiency and by limitations of transfer lines used to convey theore-containing slurry effectively through an extraction unit operation.

The polysilicate microgel is typically added in an amount of 25 to 5000g per metric ton of the oil sands ore.

One or more of the following additives may be added to the oil sands oreslurry prior to contacting with the polysilicate microgel (extractionstep (b)): anionic polyacrylamide and other polymeric flocculants andcoagulants; caustics such as sodium hydroxide, sodium silicate, andsodium citrate; organic acids and salts of organic acids, such asglycolic acid and sodium glycolate, surfactants, buffers such asbicarbonates, and antimicrobial agents.

In the extraction step (b), the oil sands ore, microgel and water aremixed and optionally contacted with air, generally in the form of airbubbles, in a reaction vessel or in a transport line. Contact of the airbubbles with the slurry results in bitumen floating to the top of theslurry, creating a top layer, referred to as a froth, or a first froth,if multiple froths are produced in the process. The (first) frothcomprises bitumen that has floated to the top of the slurry, and alsocomprises clay fines.

After forming a froth, the remainder of the slurry is permitted toseparate in the reaction vessel or is transferred from a transport lineto a separating vessel. The majority of the sand and clay fines settleto the bottom of the slurry forming a bottom layer, referred to as acoarse tailings. A middle layer is also formed in the slurry. The middlelayer is a diluted portion of the slurry comprising bitumen that did notfloat to the top and sand and clay fines that did not settle to thebottom, and is referred to as middlings.

The middlings may be removed from the middle of the reaction orseparation vessel. The removed middlings may be further processed bycontacting with air as air bubbles or passing through one or more airflotation cells, where air bubbles enhance separation of the bitumendroplets from the solids (sand and clay fines) and water of themiddlings, producing a (second) froth. The second froth may be recoverede.g., from the air flotation cell(s), and may be combined with a firstfroth. Polysilicate microgel may be added at this process step,typically in an amount of 25 to 5000 g per metric ton of the oil sandsore. Alternatively, the second froth may be added to the slurrycomprising the oil sands ore and water prior to treating the slurry toproduce the first froth.

After forming the second froth, the remainder of the slurry is permittedto separate in the reaction vessel or is transferred to a separatingvessel. The majority of the sand and clay fines settle to the bottom ofthe slurry forming a bottom layer, referred to as a fine tailings, whichcomprise less sand and more fines than coarse tailings. A middle layermay also form in the slurry. Both the middle and bottom layers may becombined and treated downstream in a dewatering step as fine tailings.

Optionally, the middle layer that is formed with the second froth isremoved as a second middlings and further treated with air in the samemanner as the (first) middlings, that is, treated with air to produce athird froth. The third froth may be combined with the first froth andsecond froth to recover bitumen. The third froth may added to the slurrycomprising the oil sands ore and water prior to producing first froth,optionally being combined with the second froth. In still anotheralternative, the third froth may be combined with the middlings prior tocontacting the middlings with air. A second fine tailings is alsoproduced with the third froth.

Each successive formation of a froth removes more of the bitumen fromthe oil sands ore. Although producing only up to a third froth isdescribed herein, successive froths (fourth, fifth, etc.) arecontemplated within the scope of this invention.

The process may further comprise removing the froth from the top of theslurry in the extraction step(s) and transferring the froth to a frothtreatment unit. In the froth treatment unit, the froth is contacted witha solvent to extract the bitumen from the froth and to concentrate thebitumen. Typically the solvent is selected from the group consisting ofparaffinic C₅ to C₈ n-alkanes and naphthenic solvents. Naphthenicsolvents are typically coker naphtha and hydrotreated naphtha having anend boiling point less than 125° C. A by-product from froth treatmentunit is froth treatment tailings, which comprise very fine solids,hydrocarbons and water.

After treatment of the froth in the froth treatment unit, theconcentrated bitumen product may be further processed to purify thebitumen.

The froth treatment tailings may be further treated in a dewatering stepto remove water, which may be recycled in the process, from the solidswhich comprise clay fines and sand.

The process may further comprise dewatering tailings. The tailings canbe one or more of any of the tailings streams produced in a process toextract bitumen from an oil sands ore. The tailings is one or more ofthe coarse tailings, fine tailings and froth treatment tailings. Thetailings may be combined into a single tailings stream for dewatering oreach tailings stream may be dewatered individually. Depending on thecomposition of the tailings stream, the additives may change,concentrations of additives may change, and the sequence of adding theadditives may change. Such changes may be determined from experiencewith different tailings streams compositions.

The tailings stream comprises at least one of the coarse tailings, finetailings and froth treatment tailings. This dewatering step comprisescontacting the tailings stream with polyacrylamide and one or both of(i) a multivalent metal compound and (ii) a low molecular weightcationic organic polymer. The tailings stream may comprise polysilicatemicrogel from the extraction steps. Additional polysilicate microgel maybe added as necessary. Polysilicate microgels enhance the flocculationof the sand and clay fines in the dewatering step by providing a betterseparation of solids from water and/or an increased rate of separationof the solids from water and/or permitting a range of operatingconditions for the dewatering step which can be tolerated while stillachieving a desired level of separation of solids from water within adesired period of time.

Dewatering may be accomplished by means known to those skilled in theart. Such means include use of thickeners, hydrocyclones and/orcentrifuges, or by decantation and/or filtration. The dewatered solidsshould be handled in compliance with governmental regulations. Theseparated water may be recycled to the process (“recycled water”). Forexample, the recycled water may be added to crushed oil sands ore forbitumen extraction. Recycled water may also be added to the process atany point where water is added.

Conventionally fine tailings and froth treatment tailings have beendifficult to dewater effectively. Both comprise clay fines andunextracted bitumen. Such tailings after dewatering, have been sent totailings pond and after time become mature fine tailings. In the presentinvention, separation of solids from even the fine tailings and frothtreatment tailings is improved.

In alternatives to the process of this invention, there is a process toextract bitumen from a slurry comprising bitumen wherein the processcomprises providing a slurry comprising bitumen, wherein the slurry is amiddlings, a fine tailings or a froth treatment tailings, contacting theslurry with a polysilicate microgel to extract bitumen from the slurry,and produce a froth comprising bitumen and tailings. Preferably thetailings are dewatered. The contacting, extracting and dewatering stepsare performed as described hereinabove.

The processes of this invention can be used to treat poor quality ores.Alternatively, a higher percentage of poor quality ores may be blendedwith good quality ores in the extraction and dewatering processes ofthis invention.

In a second embodiment of this invention, there is provided a processfor treating a tailings stream comprising sand, clay fines and water,which process comprises (a) contacting the tailings stream with apolysilicate microgel, an anionic polyacrylamide, and one or both of amultivalent metal compound and a low molecular weight cationic organicpolymer to produce flocculated solids; and (b) separating theflocculated solids from the stream. The separating step may be bydewatering. In this process, the sand and clay fines are flocculated toproduce flocculated solids. In the separating step, the flocculatedsolids are separated from the stream, e.g., by dewatering to provide thesolids and a recovered water.

The tailings stream may be a coarse tailings, fine tailings, frothtreatment tailings or a combination of two or more thereof. Processes toproduce such tailings streams are described hereinabove, with theexception that, in this embodiment, no polysilicate microgel is added inthe extraction process. Therefore, tailings streams applicable to thisembodiment can be produced from conventional oil sands processes forbitumen extraction. For example, the tailings stream treated herein canbe a slurry comprising clay fines recovered from an oil sands solventrecovery unit. Still further, as an alternative, the tailings stream maybe a mature fine tailings that has been removed from a tailings pond.

In the separating step, the objective is to flocculate and dewater thesolids, while enabling recovery of as much water as possible.Surprisingly in the present invention, a faster separation rate and morecomplete separation of the solids from the water has been achieved. Thusthe present invention has an improved process efficiency relative toconventional processes for treating tailings streams.

Solids may be disposed of, sent to a tailings pond for additionalsettling or, when solids are a concentrated source of minerals, such astitanium and zirconium minerals, the solids may be used as a rawmaterial or feed to produce for example, titanium and zirconiumcompounds for commercial products.

Order of addition of polysilicate microgel, anionic polyacrylamide andone or both of a multivalent metal compound and a low molecular weightcationic organic polymer may be varied to induce certain desiredeffects. For example, the multivalent metal compound and/or lowmolecular weight cationic organic polymer may be added first and thenthe polyacrylamide may be added to the tailings stream, that is, firstadd metal compound, then add polymer. In an alternative method, thefollowing addition sequence is used: (1) a first polymer, which is apolyacrylamide, then (2) a multivalent metal compound and/or lowmolecular weight cationic organic polymer, then (3) a second polymer,which is a polyacrylamide, are added in that sequence to the tailingsstream. The first and second polymer may be the same or differentpolymers. For example, both the first and second polymers may bepolyacrylamide; however the first polymer is an anionic polyacrylamideand the second may be a cationic polyacrylamide. In either of theaddition methods disclosed, polysilicate microgel may be added at anypoint. That is, the microgel may be added prior to or after addition ofanionic polyacrylamide and multivalent metal compound and/or lowmolecular weight cationic organic polymer, that is, prior to or afteradditions of (1), (2) and (3).

Dewatering may be accomplished by means known to those skilled in theart to separate the solids from the process water. Such means includethickener, hydrocyclone, centrifuge, decanting, and filtration. Thedewatered solids should be handled in compliance with governmentalregulations.

It has been surprisingly found that polysilicate microgels enhance theflocculation of the sand and clay fines in the dewatering step oftailings produced in the extraction of bitumen from oil sand oresrelative to known processes which use polyacrylamide alone andpolyacrylamide in combination with metal salts. Specifically, in theprocesses of this invention, solids separate from water at faster ratesthan known processes. In addition, a higher percentage of water isrecovered from the processes and the recovered water can be recycled tothe process.

It is desirable to recycle water to oil sands ore extraction andrecovery processes in order to minimize the need to use fresh water asmake-up in the processes. The recycled water may be added to crushed oilsand ore to produce a slurry for bitumen extraction. Alternatively, ifrecovered water is in excess of what is needed for the process, thewater may be returned to the environment if the water meets localstandards.

Still further, relative to known processes which use sodium silicate,the addition of polysilicate microgel during the extraction steps, doesnot adversely affect the dewatering step, that is, it has been reportedthat the presence of sodium silicate retards flocculation and separationof solids from the tailings streams. Surprisingly in this invention, theaddition of polysilicate microgel does not have a similar effect assodium silicate. Use of sodium silicate also reduces water volume thatis recovered and slows the rate of separation of solids from waterrelative to use of polysilicate microgels.

The processes of the present invention are robust and can be used toachieve desired levels of bitumen extraction and water recovery fromboth good and poor quality ores. Furthermore, the present inventionprovides a simpler separation process overall, reducing equipment, forexample, eliminating the need for mechanical separation equipment. Stillfurther the processes of the present invention may be used to treat finetailings, to recover bitumen from such tailings, and to provide amineral source, reducing the need for settling ponds.

Treatment of Tailings Stream

In a third alternative embodiment of this invention, there is a processfor the treating a tailings stream comprising (a) contacting a silicatesource and an activator with said tailings stream, (b) entrapping fineclay and sand within a silica gel, (c) spreading the silica gel over asurface, and (d) allowing the silica gel to dry to produce a trafficablesurface, wherein the silicate source is an alkali metal silicate,polysilicate microgel, or combinations thereof and wherein the tailingsstream comprises water, fine clays and sands, wherein 20% by volume toabout 100% by volume of the fine clays and sand have a particle sizeless than 0.05 mm. Optionally, the tailings stream further comprisespolysilicate microgels. Optionally the treated tailings can becentrifuged or subjected to other known dewatering techniques prior tostep (c) spreading the entrapped fine clays and sand over a surface.

The tailings stream comprises water, sand, and clay fines and optionallypolysilicate microgels. These tailings stream may be from a tailingsponds produced from fine tailings and froth treatment tailings that havebeen dewatered and deposited into the ponds and allowed to settle overtime. The tailings stream may also be from a bitumen recovery process asa fresh tailings. Fresh tailings are generally thickened withpolyacrylamides and may include sand and/or polysilicate microgelsproducing a tailings stream. The tailings stream can also containresidual polysilicate microgels from the bitumen recovery process.

The process for the treating a tailings stream comprising contacting asilicate source and an activator with said tailings stream may beadjusted to vary gelation times. Adjustments include, but not limitedto, varying the order of addition and/or concentration of the silicatesource and/or activators. For example, adding an increase of alkalimetal silicate to a tailings stream may decrease yield stress over ashort term (0.5 to 30 hours) but may result in a similar or largerincrease in overall yield stress after time. Gelation time can also bevaried by making adjustments to pH, by varying the order of additionand/or concentration of activator or activators relative to the silicatesource.

The tailings stream are contacted with a silicate source and one or moreactivators, and optionally polysilicate microgels, and form a silica gelstructure. Polysilicate microgels are as described above. Once dry, thegel becomes a hard solid with a trafficable surface. The process may beadjusted to control the gelation time. Gelation time is the time neededfor the silicate source to form a solid, gel-like structure. Preferably,the tailings stream is contacted with a silicate source and an activatorprior to being applied to a surface where gelation occurs forming athin, solid surface which is trafficable. This process of applying theproduct of contacting a tailings stream with a silicate source and anactivator to a surface may be repeated numerous times, producing a liftof several layers of hard, solid silica gel that encompass the sand andclay fines of the tailings stream.

Ideally, silica entrapped tailings formed from this process, are spreadon a sloped surface and allowed to dry. Drying occurs by air drying(evaporation), water run off, or both. If water run off occurs, one mayrecover the water from this process and recycle the run off water, suchas for re-use of the recovered water in either bitumen extraction or inthe flocculation of the tailings streams discussed infra.

The process of treating tailings stream can occur in various ways. Thesilicate source and activator can be added directly to the tailingsstream in a tailings ponds and the water is allowed to evaporate. Thetailings stream, silicate source, and activator can be mixed in a vesseland spread on a surface and allowed to dry. The tailings stream,silicate source and activator can be mixed and centrifuged to enhanceseparation with a reduced amount of silicate source and activatorneeded. Preferably, the silicate source, activator, and tailings streammay be combined in a transfer line prior to being spread on a surfaceand allowed to dry.

In a fourth embodiment of this invention, there is a process for thetreating a tailings stream comprising contacting an alkali metalsilicate with said tailings stream. Adding alkali metal silicate aloneallows the reduction of solids concentration without gelation of themixture. This is useful for treating of tailings streams where residualbitumen remains in the tailings stream. Adding alkali metal silicatealone will further disperse the suspend solids and enhance releasing ofthe residual bitumen. It is also useful for instances where a solidproduct is not immediately needed, possibly for transportation to alocation, where future treatment or storage can occur. The enhancementof bitumen recovery and reduction of solids by the addition of silicatewill also occur at higher pH levels, by adding a caustic or by usinglower ratios of the alkali metal silicate.

The processes of the present invention are robust and can be used toachieve desired levels of bitumen extraction and water recovery fromboth good and poor quality ores. Furthermore, the present inventionprovides a simpler separation process overall, reducing equipment, forexample, eliminating the need for mechanical separation equipment. Stillfurther the processes of the present invention may be used to treat finetailings, to recover bitumen from such tailings, and to provide amineral source, reducing the need for settling ponds.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 is a process flow diagram of a bitumen extraction process andprocess for tailings flocculation in accordance with this invention.

Polysilicate microgel (PSM) and crushed oil sands ore (Ore) are combinedin pipeline 1 and transferred as feed 2 to mixing vessel 3. Water isadded to mixing vessel 3, producing a slurry. Air is added to slurry inmixing vessel 3 to produce (1) first froth 4, which comprises bitumenand separates from the slurry to the top of mixing vessel 3; (2) coarsetailings 5, which comprises the majority of sand and clay fines fromfeed 2, and separates to the bottom of mixing vessel 3; and (3)middlings 6, which comprises bitumen, clay fines and sand, and is themiddle layer in mixing vessel 3.

First froth 4 is transferred to froth treatment vessel 7. Solvent isadded to treatment vessel 7 to extract bitumen 8 from first froth andalso produce froth treatment tailings 9 in treatment vessel 7. Bitumen 8is transferred from treatment vessel 7 for further processing. Frothtreatment tailings 9 comprises water and clay fines, and is furthertreated with other tailings streams.

Middlings 6 are removed from the middle of mixing vessel 3 andtransferred to second mixing vessel 3 a. Water is added to second mixingvessel 3 a. Air is added to second mixing vessel 3 a to produce secondfroth 4 a, which comprises bitumen, clay fines and water and separatesfrom middlings 6 to the top of mixing vessel 3 a, and fine tailings 10,which comprises sand, clay fines and water and separates to the lowerpart of mixing vessel 3 a. Second froth 4 a is combined with first froth4 and transferred to froth treatment vessel 7.

Coarse tailings 5 comprising sand, clay fines and water are combinedwith froth treatment tailings 9 and fine tailings 10 to provide combinedtailings stream 11 and transferred to separator 12.

Optionally, a metal compound and/or a low molecular weight cationicorganic polymer (MC/P), polyacrylamide (PAM) and polysilicate microgel(PSM) are added to combined tailings stream in separator 12. Combinedtailings stream 11 is allowed to settle in separator 12. Solids 13comprising sand and clay fines are separated from water 14. Solids 13are transferred to tailings pond. Water 14 may be recycled, such as bytransferring to mixing vessel 3 for re-use.

EXAMPLES Materials and Test Methods Materials

Mature fine tailings used in the following examples were obtained froman oil sands processor in Alberta, Canada. The solids concentrationswere 29.2 to 29.9% on a weight basis. The mature fine tailings had amedian particle size of 12.95 μm and a mean particle size of 20.9 μm and100% of the particles are finer than 0.05 mm. Yield stress measurementsof the samples were obtained by using a Brookfield rheometer equippedwith a vane spindle and results were reported in Pa (pascals). Thesodium silicate ratio used in the following examples had a ratio of 3.22SiO₂:Na₂O.

Examples 1-3

Examples 1 though 3 illustrate the increase in yield stress by additionof sodium silicate and an activator. The mature fine tailings (1000 g)were at 29.9 wt % solids, pH 7.98, and had an initial yield stress of3.7. The mature fine tailings were mixed in a reactor at 600 rpm with apropeller mixer while the activator, carbon dioxide (6 psi), was bubbledthrough a fitted disk. After 10 minutes, the pH was 6.35. Carbon dioxidewas continued to be bubbled through the mature fine tailings for anadditional 60 minutes. The pH was measured again and was 6.35. Themature fine tailings were then split into 3 portions and used forExamples 1-3.

Example 1

Example 1 illustrates the effects of sodium silicate on mature finetailings. Carbon dioxide saturated mature fine tailings (200 g) andsodium silicate (1.18 g, 3.22 ratio sodium silicate) were mixed in a 100mL Tripour beaker for 30 minutes. After 30 minutes of standing, the pHof the mixture was 7.42. The yield stress was measured at 30 minutes, 18hours, and 6 days. Results are listed in Table 1.

Example 2

Example 2 illustrates the effects of sodium silicate and an alkalineearth metal salt on yield stress. Carbon dioxide saturated mature finetailings (200 g), sodium silicate (1.18 g, 3.22 ratio sodium silicate),and calcium sulfate (0.22 g) were mixed in a 100 mL Tripour beaker for30 minutes. After 30 minutes of standing, the pH of the mixture was7.78. The yield stress was measured at 30 minutes, 18 hours, and 6 days.Results are listed in Table 1.

Example 3

Example 3 illustrates the effects of increased sodium silicate on yieldstress. Carbon dioxide saturated mature fine tailings (200 g), sodiumsilicate (2.36, 3.22 ratio sodium silicate), and calcium sulfate (0.22g) were mixed in a 100 mL Tripour beaker for 30 minutes. After 30minutes of standing, the pH of the mixture was 8.72. The yield stresswas measured at 30 minutes, 18 hours, and 6 days. Results are listed inTable 1.

TABLE 1 Example 1 Example 2 Example 3 Sodium silicate (g) 1.18 1.18 2.36CaSO₄ (g) 0 0.22 0 pH 7.42 7.78 8.72 Yield stress (Pa) After 30 minutes184 198 21 After 18 hours 458 435 128 After 6 days 1282 1117 1165

As can be seen in Table 1, the yield stress was increased by theaddition of sodium silicate and optionally calcium sulfate over time.Example 1 contained only sodium silicate and CO₂ as the activator.Examples 2 contained sodium silicate and both CO₂ and calcium sulfate.Example 2 had similar yield stress over the time tested. Example 3contained sodium silicate and both CO₂ and calcium sulfate. Example 3illustrates the effect of increased sodium silicate resulting in anincreased pH. The initial 30 minute and 18 hour yield stressmeasurements showed significantly lower yield stress but the 6 day yieldstress measurement remained consistent with Examples 1 and 2. This isbeneficial if immediate hardening of the treated mature fine tailingswas not desired. The increase in pH slows the gel rate of the mixtureallowing for a longer period of time for fluidity.

Example 4

Example 4 illustrates the effect of addition of sodium silicate and anorganic compound on yield stress. Mature fine tailings (29.9 wt %, pH7.98, yield stress of 3.7), sodium silicate (21.60 g) and ethyl acetate(4.12 g) were mixed in a 100 mL Tripour beaker. The beaker was storedfor 20 hours. After 20 hours, the yield stress was 896 Pa.

Example 5-7

Examples 5 though 7 illustrate the effect of gel time and weight loss bycontacting the mature fine tailings with sodium silicate and calciumsalts.

Example 5

Mature fine tailings (100 g, 29.2 wt % solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasadjusted with sulfuric acid to pH 7. The resulting mixture was thentested for weight loss after storing at 120 hours, 168 hours, 192 hours,and 264 hours. Results are listed in Table 2.

Example 6

Mature fine tailings (100 g, 29.2 wt % solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasadjusted with sulfuric acid to pH 7. Calcium chloride (1.78 g) was addedand mixed thoroughly. The resulting mixture had a pH of 7.1 and wastested for weight loss after storing at 120 hours, 168 hours, 192 hours,and 264 hours. Results are listed in Table 2.

Example 7

Mature fine tailings (100 g, 29.2% wt solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasadjusted with sulfuric acid to pH 7. Calcium sulfate (1.6 g) was addedand mixed thoroughly. The resulting mixture had a pH of 7.22 and wastested for weight loss after storing at 120 hours, 168 hours, 192 hours,and 264 hours. Results are listed in Table 2.

As can be seen in Table 2, the gel times can be adjusted by addition ofcalcium salts. The addition of calcium salts provide for immediate geltimes when compared to a mixture with no salt added. The resultingweight losses were similar for all three.

TABLE 2 Example 5 Example 6 Example 7 CaCl₂ (g) 0 1.78 0 CaSO₄ (g) 0 01.6 Gel time 30 minutes Instant Instant Weight loss (g) After 120 hours12.5 12.5 13.5 After 168 hours 21.2 21.4 22.9 After 192 hours 23.9 24.225.9 After 264 hours 32.2 33.0 35.4

Examples 8-11

Examples 8 though 11 illustrate the gelling of the mature fine tailingswith calcium salts without the addition of an acid to adjust pH.

Example 8

Mature fine tailings (100 g, 29.2 wt % solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasrecorded in Table 3. Calcium chloride (3.56 g) was added and mixedthoroughly. The resulting mixture had a pH of 7.15 and was tested forgel time and weight loss after storing at 120 hours, 168 hours, 192hours, and 264 hours. Results are listed in Table 3.

Example 9

Mature fine tailings (100 g, 29.2 wt % solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasrecorded in Table 3. Calcium sulfate (3.2 g) was added and mixedthoroughly. The resulting mixture had a pH of 9.91 and was tested forgel time and weight loss after storing at 120 hours, 168 hours, 192hours, and 264 hours. Results are listed in Table 3.

Example 10

Mature fine tailings (100 g, 29.2 wt % solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasrecorded in Table 3. Calcium chloride (1.78 g) was added and mixedthoroughly. The resulting mixture had a pH of 7.15 and was tested forgel time and weight loss after storing at 120 hours, 168 hours, 192hours, and 264 hours. Results are listed in Table 3.

Example 11

Mature fine tailings (100 g, 29.2 wt % solids) were mixed with sodiumsilicate (1.25 g) in a 100 mL Tripour beaker, and the final pH wasrecorded in Table 3. Calcium sulfate (1.6 g) was added and mixedthoroughly. The resulting mixture had a pH of 7.15 and was then testedfor gel time and weight loss at after storing 120 hours, 168 hours, 192hours, and 264 hours. Results are listed in Table 3.

As can be seen in Table 3, mature fine tailings can be gelled withsodium silicates and calcium salts and without pH adjustments. Weightloss amounts are comparable to Examples 5-7, where the pH was adjusted.

TABLE 3 Example 8 Example 9 Example 10 Example 11 CaCl₂ (g) 3.56 0 1.780 CaSO₄ (g) 0 3.2 0 1.6 Gel time ** Instant ** 30 minutes pH 7.15 9.918.06 9.97 Weight loss (g) After 120 hrs 16.8 18.1 17.9 14.4 After 168hrs 25.3 28.3 28.1 24.1 After 192 hrs 27.9 31.2 29.4 26.9 After 264 hrs36 39.6 37.3 35.4 ** gel time could not be determined due to water wasexuded to the surface

Examples 12-18

Examples 12 through 18 demonstrate weight loss over time of pH adjustedmature fine tailing solution with varying amounts of sodium silicate andcalcium sulfate.

Example 12

Mature fine tailings (450 g, 29.2 wt % solids) were added to a beaker.The pH was adjusted with sulfuric acid to pH 7. Sodium silicate (5.63 g)and calcium sulfate (0.90 g) were added to the beaker. The mixture wassplit into 4 separate 100 mL Tripour beakers. Two of the beakers (12 aand 12 b) were placed in a laboratory hood and two beakers (12 c and 12d) were stored on a normal laboratory bench. The weight loss wasmeasured at 2 days, 3 days, ad 6 days. Results are listed as an averageof the samples (samples a and b were averaged for the hood samples andsamples c and d were averaged for the bench samples) in Table 4.

Example 13

Example 13 is a repeat of Example 12 with reduced concentration ofcalcium sulfate (0.45 g). Results are listed in Table 4.

Example 14

Example 14 is a repeat of Example 12 with reduced concentration ofcalcium sulfate (0.23 g). Results are listed in Table 4.

Example 15

Example 15 is a repeat of Example 12 with reduced concentration ofsodium silicate (2.80 g). Results are listed in Table 4.

Example 16

Example 16 is a repeat of Example 15 with reduced concentration ofcalcium sulfate (0.45 g). Results are listed in Table 4.

Example 17

Example 17 is a repeat of Example 12 with reduced concentration ofsodium silicate (1.40 g). Results are listed in Table 4.

Example 18

Example 18 is a repeat of Example 17 with reduced concentration ofcalcium sulfate (0.45 g). Results are listed in Table 4.

Example 19

Example 19 is a repeat of Example 14 with the addition of gypsum (0.23g) prior to the addition of sodium silicate.

Comparative Example A

Comparative Example A is a water sample split into 4 samples. Thesamples were exposed to the same conditions as Example 12 with 2 samplesaveraged for the hood and 2 samples averaged for the bench test. Resultsare listed in Table 4.

As seen in Table 4, various amounts of sodium silicate and calciumsulfate can be used in the present invention with excellent results.Surprisingly, when adding the sodium silicate and calcium sulfates,weight loss was increased compared to the water sample when exposed tothe same air conditions.

TABLE 4 Comp. Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex.19^(#) Ex. A* Sodium silicate (g) 5.63 5.63 5.63 2.80 2.80 1.40 1.405.63 0 CaSO₄ (g) 0.90 0.45 0.23 0.90 0.45 0.90 0.45 0.23 0 Weight loss(g) 2 days - hood 22.6 21.2 20.6 20.0 24.7 22.8 22.1 30.25 18.5 3 days -hood 36.4 33.7 30.1 33.8 33.45 32.2 30.7 40.1 24.9 6 days - hood 68.965.9 60.5 64.6 67.6 66.9 66.4 67.6 44.2 2 days - bench 7.6 6.5 6.7 6.46.35 6.15 6.0 6.2 4.8 3 days - bench 10.6 9.4 9.6 9.2 9.45 8.9 8.6 9.47.0 6 days - bench 20.2 18.7 19.0 18.8 19.2 17.7 17.5 18.8 13.7^(#)denotes a sample where gypsum was added and the sample pH was adjustafter all reactants were added *denotes water sample

Example 20

Example 20 demonstrates an increase in yield stress of mature finetailings and sand mixture with sodium silicate, and two activators.Mature fine tailings (100 g, 29.9 wt % solids) with a pH of 7.98 and ayield stress of 3.7 Pa were added to a beaker. Sand (200 g, obtainedfrom an oil sands processor in Alberta, Canada) was added to the beaker.Sodium silicate (1.25 g) was added to the beaker. The pH of the mixturewas adjusted to pH 7 with sulfuric acid. Calcium sulfate (0.2 g) wasadded to the mixture the mixture was stirred. The pH of the finalmixture was 6.83. Yield stress was measured after 1 hour and 3 hours.Results are listed in Table 5.

Comparative Example B

Comparative Example B demonstrates the yield stress of a mature finetailings and sand mixture. Mature fine tailings (100 g, 29.9 wt %solids) with a pH of 7.98 and a yield stress of 3.7 Pa were added to abeaker. Sand (200 g, obtained from an oil sands processor in Alberta,Canada) was added to the beaker. The pH of the final mixture was 8.21.Yield stress was measured after 1 hour and 3 hours. Results are listedin Table 5.

Comparative Example C

Comparative Example C demonstrates the yield stress of a mature finetailings and sand mixture adjusted with acid to pH 7 without addition ofsodium silicate. Mature fine tailings (100 g, 29.9% wt solids) with a pHof 7.98 and a yield stress of 3.7 Pa were added to a beaker. Sand (200g, obtained from an oil sands processor in Alberta, Canada) was added tothe beaker. The pH of the mixture was adjusted with sulfuric acid to 7.Yield stress was measured after 1 hour and 3 hours. Results are listedin Table 5.

Comparative Example D

Comparative Example D demonstrates the yield stress of a mature finetailings and sand mixture adjusted with acid to a pH of 7 and additionalcalcium salt added without the addition of sodium silicate. Mature finetailings (100 g, 29.9% wt solids) with a pH of 7.98 and a yield stressof 3.7 Pa were added to a beaker. Sand (200 g, obtained from an oilsands processor in Alberta, Canada) was added to the beaker. The pH ofthe mixture was adjusted to a pH of 7 with sulfuric acid. Calciumsulfate (0.2 g) was added to the mixture the mixture was stirred. The pHof the final mixture was 6.93. Yield stress was measured after 1 hourand 3 hours. Results are listed in Table 5.

As can be seen in Table 5, Example 20 shows that by treating mature finetailings and sand mixture with sodium silicate, adjusting pH to 7, thenadding calcium sulfate, the yield stress can be increased significantly(an order of magnitude or greater). Untreated mixtures of mature finetailings and sand have low yield stress. Mature fine tailings and sandmixtures where the pH was adjust to 7 also showed the same low yieldstress measurements as the untreated mixtures. Mixtures of mature finetailings and sand, with the pH adjusted to 7, then had calcium sulfateadded, had an increase in yield stress, but still is significantly lowerthan the Example 20.

TABLE 5 Example Comparative Comparative Comparative 20 Example B ExampleC Example D Sodium silicate 1.25 0 0 0 (g) pH adjusted to 7 Yes No YesYes CaSO₄ (g) 0.2 0 0 0.2 Final pH 6.83 8.2 7.0 6.93 Yield Stress (Pa) 1hour 1485 34 32 106 3 hours >1760 30 32 179

Example 21

Example 21 demonstrates the effect on gel time for mature fine tailingsand sodium silicate mixture adjusted with acid to pH 8. Mature finetailings (220 g, 29.9% wt solids) with a pH of 7.98 were added to abeaker. Sodium silicate (2.75 g) was added to the beaker. The pH of themixture was adjusted to pH 8.03 with sulfuric acid (0.5 N). The mixturegelled.

Example 22

Example 22 demonstrates the effect on gel time for a mature finetailings and sodium silicate mixture adjusted with acid to pH 9. Maturefine tailings (220 g, 29.9% wt solids) with a pH of 7.98 were added to abeaker. Sodium silicate (2.75 g) was added to the beaker. The pH of themixture was adjusted to a pH of 9.01 with sulfuric acid (0.5 N). Themixture was still fluid after 24 hours but gelled after 2 weeks.

Examples 21 and 22 show that by reducing the amount of activatoraddition, the gel formation can be prolonged for up to several days.

Example 23

Example 23 demonstrates the effect of the addition of sodium silicate tomature fine tailings without the addition of an activator. Mature finetailings (220 g, 29.9% wt solids) with a pH of 7.98 were added to abeaker. Sodium silicate (2.75 g) was added to the beaker. The pH of themixture was not adjusted. A bottom layer of solids formed after a fewhours. The resulting solids concentration suspended was 16.3%.

Example 24

Example 24 demonstrates the effect of the addition of sodium silicate tomature fine tailings, pH adjusted to 11, without the addition of anactivator. Mature fine tailings (220 g, 29.9% wt solids) with a pH of7.98 were added to a beaker. Mature fine tailings (220 g, 29.9% wtsolids) with a pH of 7.98 were added to a beaker. Sodium silicate (2.75g) was added to the beaker. The pH of the mixture was adjusted to 11.03with sodium hydroxide (1N). A bottom layer of solids formed after a fewhours. The resulting solids concentration suspended was 15.6%.

Example 25

Example 25 demonstrates the effect of the addition of sodium silicate tomature fine tailings, pH adjusted to 12, without the addition of anactivator. Mature fine tailings (220 g, 29.9 wt % solids) with a pH of7.98 were added to a beaker. Sodium silicate (2.75 g) was added to thebeaker. The pH of the mixture was adjusted to 12.01 with sodiumhydroxide (1N). A bottom layer of solids formed after a few hours. Theresulting solids concentration suspended was 15.5%.

By adding only sodium silicate, as shown in Example 23, the mature finetailing can be modified to have a lower solids concentration compared tountreated mature fine tailings. The product is a reduced solidsconcentration mixture without gelling of the product. For Examples 24and 25 show that elevated pH will also result in a reduce solidsconcentrated mixture without producing a gelled product. A bitumen layerwas evident on the surface of the silicate treated tailings in Examples22, 23, 24, and 25.

1. A process for the treating a tailings stream comprising (a)contacting a silicate source and an activator with said tailings stream,(b) entrapping fine clay and sand within a silica gel, (c) spreading thesilica gel over a surface, and (d) allowing the silica gel to dry toproduce a trafficable surface, wherein the silicate source is an alkalimetal silicate, polysilicate microgel, or combinations thereof andwherein the tailings stream comprises water, fine clays and sands,wherein 20% by volume to about 100% by volume of the fine clays and sandhave a particle size less than 0.05 mm.
 2. A process according to claim1, wherein the activator is an acid, alkaline earth metal salt, aluminumsalt, organic ester, dialdehyde, organic carbonate, organic phosphate,amide, or a combination thereof.
 3. A process according to claim 2,wherein the activator is an acid and the acid is sulfuric acid, carbondioxide, phosphoric acid, sodium phosphate, sodium bicarbonate,hydrochloric acid, sodium hydrogen sulfate, acetic acid or a combinationthereof.
 4. A process according to claim 2 wherein the activator is anacetic ester of glycerol, glyoxal, ethylene carbonate, propylenecarbonate, formamide, or a combination thereof.
 5. A process accordingto claim 2 wherein the activator is an alkaline earth metal salt or analuminum salt and is calcium chloride, calcium oxide, calcium carbonate,calcium sulfate, magnesium sulfate, magnesium chloride, aluminumsulfate, or sodium aluminate.
 6. A process according to claim 2 whereinthe activator is an acid or an alkaline earth metal salt.
 7. A processaccording to claim 6 wherein the activator is an acid and the acid issulfuric acid or carbon dioxide.
 8. A process according to claim 6wherein the activator is an alkaline earth metal salt and the salt iscalcium sulfate or calcium chloride.
 9. A process according claim 2,wherein two or more activators are used.
 10. A process according toclaim 1, wherein the tailings stream is from a tailings pond.
 11. Aprocess according to claim 1, wherein the tailings stream is a freshtailings from a bitumen recovery process.
 12. A process according toclaim 1, wherein the silicate source, the activator and the tailingsstream are centrifuged between step (a) and step (b).
 13. A processaccording to claim 1 wherein drying in step (d) occurs by evaporation.14. A process according to claim 1 wherein the surface is sloped.
 15. Aprocess according to claim 14 wherein drying occurs by water run off.16. A process according to claim 15 wherein the water run off isrecovered and recycled.
 17. A process according to claim 1 wherein thesilicate source, activator, and tailings stream are combined in atransfer line prior to being spread on a surface and allowed to dry.